This species is a moderately sized splayfoot salamander that inhabits forest habitat, where it is often found between the leaves of bromeliads growing on trees. It has declined in the wild in recent years due to the destruction of forest within its former range by the expansion of mining operations, reducing available habitat for this species to just 15 hectares.

Urgent Conservation Actions

Conservation of the La Joya forests; surveys to determine the exact remnant range of this species; development of a Conservation Action Plan.

The Plethodontidae is by far the largest family of salamanders, comprising nearly 70% of all living species. In total there are 378 known plethodontids divided between four subfamilies and 24 genera. The plethodontids are united by the fact that they do not possess lungs and breathe entirely through their skin and mouth lining. They are often referred to as the lungless salamanders, although they are thought to have evolved from highly aquatic, lunged ancestors in the streams of the Appalachian Mountains in eastern North America. The earliest plethodontids were hypothesised to have lost their lungs because individuals with reduced, or absent, lungs were less likely to float away in the swift mountain streams where they lived. The vast majority of other salamanders possess lungs, so this makes the lungless salamanders an unusual and fascinating group of animals.

They are thought to have diverged from all other amphibian species 145 million years ago at the boundary between the Jurassic and Cretaceous periods. They are as different from all other amphibian lineages as wombats are from whales, evolving at a time when dinosaurs were still dominant. Overall, plethodontids are the most evolutionary advanced salamanders, so it may at first appear odd that they should have lost lungs, which are one of the most basic features of all vertebrates living on land. Lacking lungs and being dependent on their skin for respiration places a size restriction on these salamanders because large animals have a relatively small surface area of skin compared to their body’s volume, and have greater difficulty in supplying their body tissues with oxygen compared to smaller animals (which have a large surface area to volume ratio). The long, slender form of the lungless salamanders maximises the surface area available for gas exchange, and some species grow to lengths of over 300 mm.

Plethodontid salamanders occupy a great diversity of habitats, ranging from strictly aquatic to strictly terrestrial, exploring niches as diverse as caves, trees, mountain streams, and they are also found burrowing through the earth. Dependence on their skin for breathing places limitations on where and how lungless salamanders can live. Their skin must be kept moist at all times in order for oxygen to be taken up by the blood in capillaries beneath the skin. This means plethodontids are either confined to humid areas, or must find damp hiding places and only emerge in wet weather, typically at night. The life of a lungless salamander in less humid areas, like Europe and temperate North America, therefore comprises brief periods of activity interspersed with inactive phases that are often very long. They are able to survive the periods of inactivity because they have a very low metabolic rate and low energy requirements. Able to store much of what they eat as fat, they do no need to feed very often.

A further adaptation, present among many species of the lungless salamander subfamilies named “Plethodontinae” (from East and West North America) and “Bolitoglossinae” (from tropical Central and South America), is “direct development”. This is a method of amphibian development where the larval stage (e.g. the tadpole stage in a frog’s life history) has been eliminated. Early development takes place in eggs, which may be laid in moist places away from water, and the young hatch out as miniature adults. The well known amphibian metamorphosis, most commonly appreciated in the transition from tadpole to adult frog, does not occur outside of the egg. This mean that certain lungless salamanders in these two subfamilies may live away from water bodies, allowing them to expand their ranges to new areas.

The history and characteristics of the lungless salamanders go some way to explaining their range. They are mostly found in the New World, where they are widely distributed in eastern and western North America, as well as Central and South America. However, continental drift over millions of years has also brought them to the Old World, where they are found in parts Europe (e.g. Sardinia) and Korea. The existence of the Korean crevice salamander was unknown until 2005, when its discovery was a shock to science, indicating a long history of lungless salamanders in Asia. This is the only known species is Asia, suggesting that the rate of species generation in this part of the world is very low, especially compared the the huge radiation of lungless salamander species in the New World.

There are twelve known species in the genus Chiropterotriton (commonly known as the “splayfoot salamanders”) which represent one of twelve genera present within a lungless salamander subfamily called the “Bolitoglossinae”, including all the plethodontids from Central and South America. Splayfoot salamanders are found in Central America southward to Costa Rica, with the center of abundance being in Mexico. There have formerly been up to 20 species in the Chiropterotriton genus, although recent taxonomic reorganisations have moved species into closely related groups such as Dendrotriton (the “bromeliad salamanders”) and Nototriton (the “moss salamanders”). The splayfoot salamanders are also closely related to plethodontid groups such as Bolitoglossa (the ”mushroomtongue salamanders”) and Pseudoeurycea (the “false brook salamanders”) and externally they are indistinguishable.

The genus Chiropterotriton is thought to have originated in the Early to Mid Miocene period, between 23 and ~12 million years ago. This makes splayfoot salamanders about as dissimilar to their closest relative as humans are to gibbons. Specifically, within the splayfoot salamanders the pigmy splayfoot salamander evolved more recently, diverging approximately 9 million years ago, which is well over 8 million years before the origin of modern humans. However, there is continuing uncertainty with regard to the taxonomic status (or evolutionary history) of this species.

Description

The pigmy splayfoot salamander, like all lungless salamanders in the Bolitoglossinae subfamily, possesses a slender body, long tail and prominent eyes. A distinctive feature of the plethodontid family is a narrow groove (the nasolabial groove) running from each nostril to the upper lip: its function is to carry waterborne odours from the ground into the nasal cavity. Another curious trait of the lungless salamanders are mental (from the Latin “mentum”, meaning chin) glands. These are modified mucus glands and release pheromones, which are chemicals produced by an animal to influence the behaviour of other members if its species, often with regard to breeding receptivity. During amplexus (the mating embrace), the male clasps the female (with both his arms and legs) and rubs pheromones across the female’s snout. Mental glands are sometimes visible in males as raised bumps below their lower lip.

Lungless salamanders are very small to medium in size, usually measuring between 25 to 250 mm from the tip of the nose to the end of the tail, which salamanders retain throughout their life. They are unusual among the salamanders in that some species can detach from their tail as a predator-defence mechanism (also known as tail or caudal autotomy). It is therefore not unusual to see individuls missing part or all of their tail, which they may regererate later. Lungless salamanders may have bold patterns on their skin as adults, or they may have a colouration more similar to their environment to aid camouflage. They have well-developed “costal” grooves (successive vertical grooves in the skin along the sides of the body), generally numbering between 10-20. Their limbs are slender and often have largely or completely webbed digits. Species, like the pigmy splayfoot salamander, in the genus Chiropterotriton (the “splayfoot salamanders”) are very similar in form to those in the genera Pseudoeurycea (the “false brook salamanders”) and Bolitoglossa (the “mushroomtongue salamanders”).

The pigmy splayfoot salamander is a moderately small species, measuring around 75 mm in length (with its long tail accounting for over 40 mm of this total). The head, at a maximum width of 6 mm, is broader than the body. The nostrils are small and the snout is flat and narrowed. There are 11 distinct “costal” grooves present in the skin along either side of the body, and about 36 indistinct grooves along the sides of the tail. The skin itself is smooth.

The limbs are large and well-developed, with the hands and feet spread wide, accounting for the common name of genus, which is the “splayfoot salamanders”. The digits are very wide, rounded at the tip and slightly webbed. The dorsal (or upper) surface of this species is brownish with an indistinct darker spotted pattern. The ventral (or lower) surface is whitish, and on closer inspection is actually evenly pigmented black dots on a creamy background. Two short cream diagonal lines may be seen on the dorsal surface at the base of the tail. Colour patterns vary considerably between individuals.

Ecology

Splayfoot salamanders inhabit sub-tropical evergreen forests, damp mountain forests, and caves.
They are comparable in terms of their natural history to members of the Bolitoglossa (”mushroomtongue salamanders”) and Pseudoeurycea (“false brook salamanders”) in that they are partially terrestrial (ground dwelling) and also arboreal (tree-dwelling), and are often found in bromeliads. Bromeliads are a common type of plant from the Neotropics which possess overlapping leaves that may trap water and organic debris, providing a habitat for numerous species of invertebrate, amphibian and other creatures. They are often found growing on trees, attaching by structural roots to branches or bark.

Direct development of the young occurs within the eggs and they hatch as miniature adults. This whole process is independent of a water body since the eggs are laid in damp locations on the land, making this a truly terrestrial (or land-dwelling) species. Some species in this genus are known to display courtship rituals. The pheromone releasing mental gland on the chin of male splayfoot salamanders plays an important role in mating to influence the receptivity of females. During amplexus (the mating embrace), the male clasps the female with both his arms and legs, and rubs pheromones across the female’s snout. Females of some splayfoot salamander species have been found to guard the eggs throughout their development, often in special hides, until hatching occurs.

Splayfoot salamanders may at first appear very vulnerable to predators but a number of defense mechanisms have been found among the members of this genus. These include noxious skin secretions; aposematic colouration of the back (striking skin patterns to warn away potential attackers); and caudal autotomy (the ability to drop the end of the tail and later regrow it) and behavioural defensive methods, including biting, immobile posture, coiling and flipping of the body, and displays where the stomach is exposed and the tail is held up or undulated.

Habitat

The pigmy splayfoot salamander lives in bromeliads in pine-oak and cloud forests, which are also described as subtropical or tropical moist montane forests. This species can survive in disturbed and degraded forest habitats, although it is dependent upon the presence of trees.

Distribution

This species is known only from La Joya in central-western Veracruz, Mexico, at an altitude of 1,200 metres above sea level.

The pigmy splayfoot salamander is moderately abundant in its tiny range, although its population does appear to have declined recently, most likely due to loss of suitable forested habitat.

Population Trend

The IUCN Red List of Threatened Species indicates that the total population size of the pigmy splayfoot salamander is generally in decline.

Status

The pigmy splayfoot salamander is listed as Critically Endangered in the IUCN Red List of Threatened Species because its extent of occurrence is less than 100 km sq. and its area of occupancy is less than 10 km sq., all individuals are in a single location, and there is a continuing decline in the extent and quality of its habitat at La Joya. In addition, this species is protected by Mexican Law under the "Special Protection" (Pr) category.

Threats

All areas surrounding the pigmy splayfoot’s only known habitat in La Joya are highly disturbed by extensive logging and mining. Catastrophically for this species’ wild habitat, the area of forest available for this species was halved between 2003 and 2004 due to the expansion of mining activities. In 2004 the remaining available habitat for this species was only about 15 hectares in 2004.

Conservation Underway

This species is not known from any protected areas, and there are currently no conservation measures underway for this species, although it is protected by Mexican Law under the "Special Protection" (Pr) category.

Establish spatial knowledge of the distribution and occurrence of some of the threatened species in Mexico.

Screen individuals and other amphibians in these areas for the presence of chytrid fungus.

Increase the capacity in Mexico for the long term conservation of these species

Conservation Proposed

The most urgent measure required to protect this species is the conservation and protection of the La Joya forests. Further field surveys should be conducted to determine the exact remnant range of this species and all information collected should then form the basis of a Conservation Action Plan for the protection of this species in the wild.

In addition to conserving wild habitat for this species, the IUCN Technical Guidelines for the Management of Ex situ Populations, part of the IUCN Red List of Threatened Species, recommend that all Critically Endangered species should have an ex situ population managed to guard against the extinction of the species. An ex situ population is ideally a breeding colony of a species maintained outside of its natural habitat, giving rise to individuals from that species that are sheltered from problems associated with their situation in the wild. This can be located within the species’ range or in a foreign country that has the facilities to support a captive breeding programme for that species. Further investigation is therefore required into the possibilities of establishing a captive breeding programme for the pigmy splayfoot salamander. Captive animals could then be a source of new individuals to repopulate protected habitat.

Parra-Olea, G., Papenfuss, T.J. and Wake, D.B. 2001. New species of lungless salamanders of the genus Pseudoeurycea (Amphibia: Caudata: Plethodontidae) from Veracruz, Mexico. Scientific papers of the Natural History Museum of the University of Kansas 20: 1-9.